In photolithography techniques, for example, a resist film composed of a resist composition is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a photomask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist composition in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist composition in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers (248 nm) have been introduced, and ArF excimer lasers (193 nm) are now also starting to be introduced. Furthermore, research is also being conducted into lithography techniques that use exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers (157 nm), extreme ultraviolet radiation (EUV), electron beam, and X ray.
Reproduction of patterns with very fine dimensions requires resist materials with high resolution. As such resist materials, chemically amplified resist compositions are used, which include a base resin and an acid generator that generates acid upon exposure. For example, a chemically amplified positive resist contains a resin component in which the alkali solubility increases by the action of an acid and an acid generator component that generates acid upon exposure, and when an acid is generated from the acid generator by exposure in the formation of a resist pattern, the exposed portions become alkali soluble.
Typically, resins such as polyhydroxystyrene (PHS) based resins in which the hydroxyl groups have been protected with acid dissociable, dissolution inhibiting groups or resins having structural units derived from (meth)acrylic acid within the main chain (namely, an acrylic-based resin) in which the carboxyl groups have been protected with acid dissociable, dissolution inhibiting groups are used as resin components of chemically amplified positive resist compositions. Examples of acid dissociable dissolution inhibiting groups used include: the so-called acetal groups such as chain-like ether groups typified by a 1-ethoxyethyl group, and cyclic ether groups typified by a tetrahydropyranyl group; tertiary alkyl groups typified by a tert-butyl group; and tertiary alkoxycarbonyl groups typified by a tert-butoxycarbonyl group (for example, see Patent Document 1).
Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.
On the other hand, as acid generators of chemically amplified positive resist compositions, a multitude of acid generators have already been proposed. Examples thereof include onium salt-based acid generators such as iodonium salts and sulfonium salts; oxime sulfonate-based acid generators; diazomethane-based acid generators; nitrobenzylsulfonate-based acid generators; iminosulfonate-based acid generators; and disulfone-based acid generators. Currently, onium salt-based acid generators are generally used as acid generators. Of these, the onium salt-based acid generators which include a cation moiety composed of triphenylsulfonium (TPS) and an anion moiety composed of fluorinated alkylsulfonic acid ions such as nonafluorobutanesulfonate are the most widely used, since they exhibit a powerful acid-generating capability (for example, refer to Patent Document 2).
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2002-341538
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2003-241385